The present invention relates to an EGR (Exhaust Gas Recirculation) cooler and various heat exchangers having a casing.
A casing-type heat exchanger used as an EGR cooler is proposed as Japanese Patent No. 3022963. This heat exchanger is comprised, as shown in FIGS. 5 and 6, such that a core 5 is formed by penetrating both ends of a large number of flat tubes arranged in parallel through a header plate 3, the outer circumference of the core 5 is fitted with a box-state first casing 20 and a second casing 21 divided into a pair of upper and lower halves, and a joint or the like of the casings are fixed in an air tight manner by way of welding or the like. And cooling water is made to flow through either of the casing side and the header side while an exhaust gas is made to flow through the other for cooling the gas.
In a conventional casing-type heat exchanger, the upper and lower pair of box-state casings are fitted with the outer circumference of the core as shown in FIGS. 6A and 6B. At the joint portion of the casings, as shown in FIG. 6B, the lower end of the upper member is fitted to the outer circumference of the tip end portion of the lower member, and the both are joined by welding or brazing. There is no problem if the both are joined by welding, but in case of brazing, a gap 22 is generated at the joint portion as shown in FIG. 6B, which could cause defective brazing.
That is, one of the outer surfaces of the pair of box-state casings and the core part is coated by a brazing metal and the whole is integrally brazed and fixed in a furnace. However, if the gap 22 is formed at the joint, the brazing metal is biased to one side and does not penetrate into the other side, which causes lack of brazing. Thus, there has been a problem that air tightness or liquid tightness can not be maintained.
The present invention has an object to prevent occurrence of a gap which tends to be formed in the conventional casing as less as possible and to provide a heat exchanger with reliable brazing.